Line scanning transformer with adjustable leakage inductance



Jan. 14, 1964 M. JEN'OT 3,118,122

LINE SCANNING TRANSFORMER WITH ADJUSTABLE LEAKAGE INDUCTANCE Filed Aug. 11, 1959 IVVENTOR @j M. I E N 0T Mm@ M1 6M United States Patent O 3,118,122 LINE SCANNING TRANSFORMER WITH ADJUSTABLE LEAKAGE INDUCTANCE Michel Janet, Le Raincy, France, assignor to Societe dExplnitation des Ateliers Rene Halitermeyer, Montreuil-sous-Bois, Seine, France, a corporation of France Filed Aug. 11, 1959, Ser. No. 332,992 Claims priority, application France Aug. 11, 1958 4 Claims. (Cl. 336-134) lt is known that the leakage between lthe two windings of a very high voltage line scanning transformer for television results generally in producing oscillations in the leakage inductance and in the leak-age capaci-tance between said two windings, which results in intolerable interferenoes on the image in the case of rather large amplitudes of said oscillations which persist during the scanning.

It is also known that by tuning the circuit comprising the induct-ance and leakage capacitance in the vicinity of an uneven harmonic off the line return frequency, the energy of the oscillations created in said circuit during the return time may be recovered, so as to reduce the losses in the line output stage 'and to noticeably lower the ratio between the voltages produced on the transformer primary winding duning the return and the voltages considered at the same points during the scanning.

The peak current of the output stage is then substantially reduced, which results in a very substantial reduction of the losses.

In practice, the shock excitation frequency in the tuned circuit, the voltage of which is added in the transformer to the return voltage, is advantageously set at a frequency slightly lower than that of an uneven harmonic of the line return frequency, in order to take into consideration the fact that the capacitance of the shook circuit is quickly charged and discharged by the leading and trailing edges of the return pulse, which results in highly reducing the durations of the rst `and last half-cycles of the shock voltage.

Tuning of the shock excitation frequency is generally made in the transformers wherein ythe primary winding and the very high voltage winding `are coiled on two difierent legs of the transformer core, by means of a magnetic shunt made of a small rod of ferrite which is caused to slide on a path parallel to the legs of the transformer core which support the two windings, the average value of the leakage inductance between primary and secondary Windings being preset in the factory by displacing a short-circuit ring .surrounding one or" the core legs located between the two legs on `which are coiled said primary and secondary windings.

Now, it is advantageous, for different reasons which will be developed in the course of the present disclosure, to coil the secondary winding on the sa-me leg of the magnetic circuit that the primary winding lis coiled, which reduces in particular the magnetic radiation of such transformers and the correlated disturbance of the radi-o receivers which are in the vicinity of the latter.

Thus, the present invention has for its object to provide a very high voltage line scanning transformer wherein the secondary winding is coiled outside of the primary winding, and comprising `a device permitting regulation of the value of the leakage inductance between the primary winding and the voltage step-up winding.

Said last-named device could have been made by merely providing for mechanical displacement of the secondary winding relative to the primary winding in the direction parallel to the co-re leg on which both windings are coiled.

However, such solution has not been retained in practice, since it requires using a 7 kv. tlexible connection and a special insulating element supporting a winding the ex- 'ice treme potentials of which are 7 kv. and 20 kv., respectively.

lt will be seen hereinafter in the description that the device for adjusting or setting Ithe value of the leakage inductance, is characterized by providing a free space between the primary and secondary windings obtained by ott-setting the secondary Winding relative to the magnetic core leg, a free space into which small ferrite rods may be more or less introduced, so as to modify the path of the lines of force running between lthe primary and secondary windings and thus to bring up the circuit to lthe resonance by modifying the value of the leakage inductance coil. It is quite evident that a change in the optimum position of the small ferrite rods or of the shortcircuited loop relative to the position corresponding to lthe resonance, may be used for reducing the scanning amplitude.

`Further characteristics of the present invention will be more clearly understood when reading the following description of `one ttor-m of my veiy high voltage transformer, according to this invention, given as an illustration and by no means a limitation of the present invention as defined in the appended claims, with reference to the `annexed drawings, in which:

FIG. l is a section taken `along the symmetry plane of the magnetic core of the transformer according to this invention;

PIG. 2 is a section taken yalong .II-ll in HG. l, and

FIG. 3 is ya section taken along ll--l'll in FlG. l.

In FIGS. 1, 2 and 3 there is shown the magnetic core 1 and the primary winding 2, but the secondary winding shown by the reference number 3a is Offset .from the primary winding and trom core axis, as shown in FIG. 2.

Three small rods of ferrite, designated by the reference numbers 7, 3 and 9, `are mounted inside of the apertures 1t?, il and l2.: in a moulded element 1.3 comprising on both sides of the apertures ld and 12 two insulating rods i4 and 115 acting as a support for the secondary winding 3a the internal diameter of which is realized so as to provide a free space lo between the primary winding 2 and the secondary winding 3a.

It can be seen in FIG. l that the molded element 13 has a certain thickness, so that the sima-ll rods 7, 3 and 9 sliding inside the apertures lit, il land l2 remain perfectly parallel with the core leg while moving in the free space provided between the primary and secondary windings without `any liability of untimely contact between the small rods of ferrite, which may be handled without care, and between the live windings.

lt can be seen in FIG. 3 that the apertures 1l), 11 and 12 comprise each three ribs 17 integrally molded with the element l acting as a support for the small rods, ribs by which the small rods may be maintained against any movement in a position parallel to the core axis, while permitting said small rods to be pushed down tat will without any effort being necessary to handle the same, so as to obtain an accurate tun-ing of the scattering circuit on the required lfrequency, which is slightly lower than that of an uneven harmonic such as the third harmonic for example, and then `avoid that said circuit fall out of tune.

It is evident that the form orf the invention hereinabove described is only given in an [illustrative and by no means limitative sense.

In particular, the sha e of the insulating rods integral with the molded element 13 is not necessarily round and may have any suitable contour. Also, it is not necessary that the number of the ferrite small rods be equal to three, and `the latter may have respectively different diameters, different shapes in cross-section, for example, polygonal, or even corn-prise an external threading and a slot by means of which they may be more or less pushed down by threading into the element 13.

The shape of said ribs may also be varied at will as Well as the number of these ribs which may be otherwise replaced by short studs, extra thicknesses or internal @readings which may facilitate handling of the ferrite small rods while permitting to maintain the same in position by Ifriction.

1t is to be understood that those skilied in the art may bing numerous modnications, improvements or additions, or replace some devices by their equivalents, to the forms of the invention described and shown, without departing from. the scope of the invention.

What 1 claim is:

l. A very high voltage line sweep transformer for television comprising in combination a ferrite core formed into a closed magnetic circuit, a primary coil wound around one leg of said core, a high voltage secondary coil Wound around said primary coil, the axis of said secondary coil being slightly spaced from l ut parallel to that of said primary coil so as to leave between said coils a space having a crescent-shaped cross-section, support means of insulating material mounted on `said leg, and at least one ferrite rod of substantial thickness carried by said support for displacement Within said space in a direction parallel to the axes of said coils so as to vary leakage nductance between said coils.

2. A transformer as claimed in claim 1 in which said support means is fixed on said core and is provided with a plural-ity of apertures, each of which carries a small ferrite rod mounted therein for axial movement parallel to said core.

3. A device as claimed in claim 2 in which said apertures are provided with ribs which engage relatively small sectors of the circumference of said rods.

4. A device `as claimed in yclaim 2 in which said apertures are tapped and the ferrite rods are threaded to mate with said tapped apertures.

References Cited in the file of this patent UNITED STATES PATENTS 2,340,749 Harvey Feb. 1, 1944 2,437,021 Fries Mar. '2, 1948 2,674,721 Jackson Apr. 5, 1954 2,752,578 `vl/inkel June f, 1956 2,753,532 Ashby uly 3, 1956 2,849,690- Vanhoeven Aug. 26, 1958 

1. A VERY HIGH VOLTAGE LINE SWEEP TRANSFORMER FOR TELEVISION COMPRISING IN COMBINATION A FERRITE CORE FORMED INTO A CLOSED MAGNETIC CIRCUIT, A PIMARY COIL WOUND AROUND ONE LEG OF SAID CORE, A HIGH VOLTAGE SECONDARY COIL WOULD AROUND SAID PRIMARY COIL, THE AXIS OF SAID SECONDARY COIL BEING SLIGHTLY SPACED FROMBUT PARALLEL TO THAT OF SAID PRIMARY COIL SO AS TO LEAVE BETWEEN SAID COILS A SPACE HAVING A CRESCENT-SHAPED CROSS-SECTION, SUPPORT MEANS OF INSULATING MATERIAL MOUNTED ON SAID LEG, AND AT LEAST ONE FERRITE ROD OF SUBSTANTIAL THICKNESS CARRIED BY SAID SUPPORT FOR DISPLACEMENT WITHIN SAID SPACE IN A DIRECTION PARALLEL TO THE AXES OF SAID COILS SO AS TO VARY LEAKAGE INDUCTANCE BETWEEN SAID COIL. 